The purpose of permanent or irreversible bonding of solid substrates is to produce as strong a bond as possible and especially an irreversible bond, i.e., a high bonding force between the two contact surfaces of the solid substrates. For this purpose there exist in the prior art various approaches and production methods, especially the welding of the bond or the creation of a diffusion bond between the surfaces at elevated temperatures.
All kinds of materials, but primarily metals and/or ceramics, are permanently bonded. One of the most important permanent bonding systems is a metal-metal system. In recent years Cu—Cu systems have been the primary systems gaining in popularity. The development of 3-D structures specifically requires in most cases the joining of different functional layers. This joining being done more and more often using so-called TSVs (Through Silicon Vias). Ensuring contact between these TSVs is very often done by means of copper contact points. At the time of the bonding, full-fledged, functional structures, for example, microchips, are very often already present at one or more surfaces of the solid substrates. Since different materials with different thermal expansion coefficients are used in the microchips, a rise in temperature during bonding is not desirable. Such an elevation of temperature can lead to thermal expansion and thus to thermal stresses that can destroy the parts of the microchip or its vicinity.
The known production methods and approaches taken thus far frequently lead to unreproducible or poorly reproducible results that especially can hardly be transferred to different conditions. In particular, production methods that are currently being used often employ high temperatures, i.e., temperatures above >400° C., to guarantee reproducible results.
Technical problems such as high energy consumption and possible destruction of the structures that are present on the solid substrates result from the high temperatures that have been required to date for a high bonding force.
Other requirements for a bonding process are:                Front-end-of-line compatibility.        
This is defined as the compatibility of the process during the production of the electrically active components. The bonding process must therefore be designed in such a way that active components such as transistors that are already present on the structural wafers are not compromised or damaged during processing. The compatibility criteria primarily includes purity of certain chemical elements (primarily the CMOS structures) and mechanical loading capacity, especially for loads arising from thermal stresses.                Low contamination.        No application of force, or application of as little force as possible.        Lowest possible temperature, especially in the case of materials with different thermal expansion coefficients.        
Against this backdrop there has long existed a need to create a direct, permanent connection between two metal surfaces under conditions of the lowest possible temperatures and pressures/forces. A direct permanent connection is preferably defined by one skilled in the art as the production of a completely new structure over the boundary surface between two metal surfaces that are in contact.
In this case the formation of a new structure is preferably done by recrystallization. Recrystallization is defined as the production of a new structure by means of grain growth. The prerequisites for such grain growth include high degrees of deformation that increase the dislocation density of a material and thus bring the material into an energetically metastable state; when a critical temperature is exceeded, this leads to new grain formation. In heavy industry, massive transformation processes such as rolling, forging, deep drawing, twisting, shearing, etc. are primarily used to achieve high degrees of dislocation.
Such massive transformation processes, with which the above-mentioned metastable dislocation-rich microstructure can be created at low temperature, cannot be used in the semiconductor industry because of the very thin substrates with extremely fine structures and the thin, fragile wafers. Neither the structures nor the wafers can or should be subjected to massive transformation since they will be destroyed thereby.